Since the discovery that mutations in alpha-synuclein are associated with autosomal dominant Parkinson's Disease and that this protein accumulates in cytoplasmic aggregates in multiple neurodegenerative disorders, significant efforts have been made to address its function in normal and disease states. Understanding its role(s) in the maintenance of neuronal integrity would be improved by addressing how mutant forms and altered levels of alpha-synuclein expression specifically affect cellular pathways implicated in neurodegeneration. This research therefore seeks to obtain a fuller understanding of the specific functional consequences of altered levels of expression of normal and mutant forms of alpha-synuclein. It will address this issue using a combination of methods: microarray-based gene expression profiling, quantitative RT-PCR and immunoblotting. Its specific aims are to: I. Identify which set(s) of pathways implicated in neurodegenerative disease are specifically altered in the striatum, brainstem (including the substantia nigra), hippocampus and neocortex (i.e., the brain regions affected in Parkinson's Disease) of aging transgenic mice overexpressing normal human alpha-synuclein and who exhibit motor deficits, Lewy pathology, and neuronal degeneration. II. Identify which set(s) of pathways implicated in neurodegenerative disease are specifically altered in the same regions of the brains of aging knockout mice lacking the alpha-synuclein gene who exhibit functional deficits in the nigrostriatal dopamine system. III. Quantitatively characterize how altered levels and/or forms of alpha-synuclein affect the pathways identified in Specific Aims I and II by analyzing their expression in rat PC12 cell lines stably transfected with, and conditionally expressing defined levels of, normal human and/or mutant alphaa-synuclein. An understanding of the consequences of altered alpha-synuclein function will provide for a more complete perspective of how altered levels and forms of alpha-synuclein contribute to neurodegenerative disease. This will contribute to providing a basis for the rational design of additional investigations into the molecular mechanisms underlying neurodegeneration in Parkinson's disease and will have significant potential for the design of etiologically based therapies.